Different approaches have been reported to treat presbyopic patients.16 In a recent publication,7 we reported a new type of refractive surgery, pseudoaccommodative advanced surface ablation (PASA), which is capable of compensating for presbyopia in myopic and hyperopic patients. In this article, we analyze the objective visual performance of patients 6 months after PASA surgery.
PATIENTS AND METHODS
This study comprised 62 eyes of 35 patients with 6-month follow-up that underwent primary or secondary treatments using PASA. One surgeon (R.C.) performed all cases using the NIDEK EC-5000 Software Version 1.26 (NIDEK, Gamagori, Japan). Wavefront-guided (custom) ablations were not used in this study. The surgical technique involved performing a total transepithelial laser ablation followed by a multipass conventional stromal ablation for the sphere and cylinder with pseudoaccomodative corneal ablation with the modified PASA nomogram using a previously described cooling and smoothing technique.7 Of the 62 eyes, 41 were myopic and 21 were hyperopic. Within each group, patients were separated according to age (≥40 years and <40 years).
We evaluated the pre- and postoperative results of the measurements of distance and near uncorrected visual acuity (UCVA), spherical aberration (coefficient of the Z12 Zernike polynomial), and the asphericity (Q) index. The corresponding wavefront maps (total, low, and high order aberrations) and the corresponding point spread function (PSF) and modulation transfer function (MTF) were also calculated. The coefficients of the Zernike polynomials were obtained using the NIDEK OPD-Scan V.1.12f. These were analyzed using Microsoft Office Excel 2003 (Microsoft, Redmond, Wash) and SPSS release 8.0 (SPSS, Chicago, 111) to obtain the pertinent statistical characteristics for each group. The corresponding wavefront maps and the PSF and MTF graphs were then calculated and simulated using MATLAB (The Math Works, Natick, Mass).
Figure 1. Average asphericity (Q) values for a 6~m m central cornea for myopic patients aged ≥40 years (column A), myopic patients aged <40 years (column B), and hyperopic patients aged ≥ 40 years (column C). In all cases, the preoperative 6-mm central cornea was oblate; however, postoperatively, the 6-mm central cornea was prolate.
Figure 2. Pre- and postoperative average values for the spherical aberration (Z12) for myopic patients aged ≥40 years (column A), myopic patients aged <40 years (column B), and hyperopic patients aged ≥ 40 years (column C). In the two groups aged ≥40 years, the preoperative Z12 was positive whereas in the myopic patients aged <40 years it was negative. Postoperative Z12 was negative in all groups.
Figure 3. Pre- and postoperative mean A) distance and B) near UCVA. Column A = myopic patients aged ≥40 years, column B = myopic patients aged <40 years, column C = hyperopic patients aged ≥40 years. Distant and near UCVA improved in all groups.
Our results show improvement for distant and near mean UCVA, increase in negative spherical aberration and negative asphericity index, and improvement in the corresponding MTF.
The average asphericity (Q) values for a 6-mm central cornea diameter are presented in Figure 1. Column A corresponds to the myopic patients aged ≥40 years (37 eyes) whereas column B corresponds to myopic patients aged <40 years (4 eyes). Column C corresponds to hyperopic patients aged ≥40 years (20 eyes). Note that in all cases, the postoperative value is negative, which implies a prolate corneal shape, whereas the preoperative asphericity describes an oblate cornea in every group.
Figure 2 shows the pre- and postoperative average values for the spherical aberration (Z12) for the analyzed groups. Note that the average preoperative value for patients aged ≥40 years is positive whereas for patients aged <40 it is negative. It is interesting to note that in all cases, the postoperative values are negative regardless of age.
Figure 3 shows the corresponding pre- and postoperative UCVA. Figure 3A corresponds to the mean distance UCVA, and Figure 3B corresponds to the mean near UCVA. Our results show that the average postoperative UCVA is >20/25 in all cases.
Figure 4. MTF graphs for the average total wavefront maps of the A) myopic and B) hyperopic groups. In both cases, the blue line corresponds to the average MTF profile of the preoperative group and the orange line corresponds to the average MTF profile of the postoperative group. Note that for both cases, the area under the MTF curve increases, which is directly related with an enhanced performance.
Modulation transfer function graphs of each of the four subgroups are presented in Figure 4. Figure 4A presents the performance of the average total wavefront map for the pre- and postoperative values of the myopic patients. Figure 4B shows the performance for the average total wavefront map for the pre- and postoperative values of the hyperopic patients. As expected, the postoperative performance depicted by these MTF graphs improves in both cases, mainly for the frequency values below the resolution limit of the eye (60 cycles/degree), which corroborates our previous results.
Pseudoaccommodative advanced surface ablation is a promising approach for the surgical correction of presbyopia with distance refractive error (myopia and hyperopia with or without astigmatism). This PASA technique could theoretically be used in non-presbyopic patients with refractive error or post cataract patients with monofocal intraocular lenses. The increase in negative spherical aberration and asphericity/eccentricity index seems to increase the depth of focus of the eye, improving the near vision and compensating the age-related lens changes. Rather than creating a multifocal cornea, PASA appears to create an improved aspheric (prolate) ablation profile.
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